The present invention relates to a reconfigurable filter architecture, and more particularly to a filter architecture having independently configurable gain, bandwidth, and frequency offset.
Multimode receivers are capable of receiving signals according to multiple standards such as the Global System for Mobile Communications (GSM) and Wideband Code-Division-Multiple-Access (WCDMA). In order to accommodate multiple standards, multimode receivers require a variety of different filtering options. In modern receiver architectures, received signals are downcoverted from a radio frequency (RF) to either a very low intermediate frequency (VLIF) or to DC and filtered to remove adjacent channel signals before analog to digital conversion. Filtering at a VLIF requires a filter having a bandpass response, wherein the center frequency of the filter is offset from DC, while filtering at DC requires a filter having a low-pass response. Thus, multimode receivers require separate filters having a passband at DC and at VLIF in order to filter adjacent channel signals before analog to digital conversion. Further, the adjacent channel spacing and widths vary according to standard, thereby requiring filters having varying bandwidths for each standard.
In order to accommodate the filtering requirements associated with multiple standards, multimode receivers typically include separate filters to accommodate different communication standards. However, these filters require large capacitors that consume valuable chip area. Therefore, there remains a need for a single filter architecture that is easily configurable to accommodate the different requirements of various communications standards.
The present invention provides a reconfigurable filter having a bandwidth and frequency offset that are independently configured, thereby allowing the filter to realize any filter pole. In general, the filter includes a filtering stage and a reverse gain stage. The filtering stage has a bandwidth configured by a bandwidth control signal from control logic and a frequency offset configured by an offset control signal. The reverse gain stage provides the offset control signal to the filtering stage based a reverse gain control signal from the control logic and the output signal. Based on the bandwidth control signal and the reverse gain control signal, the bandwidth of the filter is configured independently from the frequency offset of the filter and the frequency offset is configured independently from the bandwidth.
The filter may also include a forward gain stage that amplifies an input signal to provide the amplified input signal to the filtering stage. A gain of the forward gain stage is configured by a forward gain control signal from the control logic, thereby allowing the gain of the filter to be configured independently from the bandwidth and frequency offset while eliminating the need for additional amplifier stages before the filter.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.